The increased number of deep wells being drilled and the encounterments, during drilling, of abnormally high temperature gradients has led to the development of cement retarders to be used to help extend the pumpability of manufactured cements currently available. It is extremely desirable in such connection to have longer thickening times in the cementing compositions employed when they are used under high temperature conditions. These demands, oftentimes, cannot be met with presently available (including commercial) retarded cements (such as API Classes D and E).
At the present time, very few cementing compositions are used to cement wells below 12,000 feet where static temperatures are in excess of 260.degree. F., unless additional retarder is utilized. Observation of cementing compositions currently used in wells 10,000 feet and deeper indicates that a larger number of the compositions employed contain additives to modify the properties of the basic cement. These additives, in addition to retarders, can frequently be light-weight clay and equivalent mineral materials (such as bentonite, Diacel D, etc.) silica flour, heavy-weight materials (such as Hi-Dense No. 2, barite, etc.) or any of the many other materials and component additives available for altering the properties of the cement composition used.
The selection of a retarder that will be compatible with the manufactured retarded cements, which in themselves usually contain a retarder, sometimes becomes a difficult task. Compounds such as lignins (salts of lignosulfonic acid), gums, starches, various weak (oftentimes organic) acids, and cellulose derivatives have been used in the manufacture of commercial retarded cements. One of the first retarders developed in the trade was a blend of borax, boric acid and gum arabic. Due to blending problems, this retarder was exceedingly difficult to handle at bulk cement plants. Nonetheless, much actual use has been had of such retarders for commercial retarded cements prior to the time that ameliorated retarders were developed.
The primary factor and influence that governs the use of additional retarder is the temperature of the well. As the temperature increases, the chemical reaction between the cement and water is accelerated. This, in turn, reduces the thickening time or pumpability of the cement composition or paste. The use of additives with high water ratios also necessitates the use of additional retarder to obtain the desired thickening time. This can be due to one or both of the following fundamental factors, namely: (1) high surface materials, which generally have high water requirements, which adsorb part of the retarder leaving less to affect the retardation of the cement; and (2) additional water which further dilutes the concentration of retarder and thereby reduces its retarding potential.
Most currently available retarders can be used with the basic cementing compositions containing API Class A, D, or E cements, Pozmix-Cement and Pozmix 140 blended with various additives. Appropriate test data available in the art coupled with developed laboratory observations can indicate the performance of cementing compositions and the like with and without retarder when used to depths of 12,000 feet or where static temperatures are in the range of 260.degree. to 275.degree. F. Where bottom hole conditions exceed these values, it is normally recommendable that thickening time tests be made, in the laboratory, on the specific component parts of the slurry (or paste) prior to the actual cementing job. Variations in thickening times are not due solely to down hole conditions of temperature and pressure. They frequently, pragmatically speaking, may be the result of irregularities in the basic cement.
Further quite pertinent art and direction in the area of well cementing and the like practices includes the Report Prepared By The API MID-CONTINENT DISTRICT STUDY COMMITTEE ON CEMENTING PRACTICES AND TESTING OF OIL-WELL CEMENTS issued by AMERICAN PETROLEUM INSTITUTE (i.e., "API"), Division of Production, in Dallas, Texas 75201 as API Bulletin D-4, Corrected Edition of March 1963, entitled "The Effects Of Drilling-Mud Additives On Oil-Well Cements"; "API Specification For Oil-Well Cements And Cement Additives" (API Std 10A, Fourteenth Edition, dated April, 1969); and "API Recommended Practice For Testing Oil-Well Cements And Cement Additives" (API RP 10B, Sixteenth Edition, dated April, 1969).